The present invention relates to a multicontroller apparatus, a multicontroller system, a nuclear reactor protection system, an inverter control system and a diagnostic device, and in particular to a multicontroller apparatus, a multicontroller system, a nuclear reactor protection system, an inverter control system and a diagnostic device suitable for asynchronous use.
The present invention is related to U.S. Pat. application Ser. Nos. 069,170 filed on Jul. 2, 1987 and 242,170 filed on Sep. 9, 1988 now U.S. Pat. No. 4,989,129, both assigned to the assignee of the present application.
In general, in important control systems, it is attempted to raise the reliability of the whole system by providing controllers o safety-protection apparatuses with redundancy. Further, in order to raise the rate of operation of the whole control system, diagnosis of controllers provided with redundancy is made. A controller having an abnormality found by means of diagnosis is rapidly repaired.
For example, an example of a multicontroller apparatus having a diagnostic device is described in U.S. Pat. No. 4,517,154. This known multicontroller apparatus has been applied to a nuclear reactor protection system and has an online diagnostic system. That is to say, one diagnostic device is provided for four redundant controllers. This diagnostic device outputs a test signal successively to the four redundant controllers and receives answer signals from the four redundant controllers. On the basis of the answer signal fed from each controller, it is judged whether an abnormality is present in that controller or not.
If a single diagnostic device makes diagnoses of four redundant controllers, diagnosis of all of the controllers is not performed suitably when the diagnostic device itself becomes abnormal. Even if a controller is normal, it then might be judged abnormal. Even if a controller is abnormal, it might be judged normal.
A multicontroller apparatus having one diagnostic device provided for each of four redundant controllers so that one diagnostic device may make a diagnosis of one controller is described in JP-A-62-280697. Such a multicontroller apparatus eliminates the problems of the multicontroller apparatus described in U.S. Pat. No. 4,517,154.
By providing a plurality of redundant diagnostic devices as described in JP-A-62-280697, each diagnostic device can arbitrarily make a diagnosis of its corresponding controller. However, there is a possibility that diagnoses are simultaneously made of all controllers. In this case, control of a control object by controller becomes impossible. Such a state must be avoided in a nuclear reactor plant which especially requires safety.